1. Field of the Invention
The present invention relates to a zinc oxide (ZnO) precursor and a method of depositing a ZnO-based thin film using the same, and more particularly, to a ZnO precursor and a method of depositing a ZnO-based thin film using the same, with which a high-quality and high-purity ZnO-based thin film can be deposited.
2. Description of Related Art
Flat panel displays, such as a thin-film transistor liquid crystal display (TFT-LCD), a plasma display panel (PDP), a field emission display (FED), and an organic light-emitting device (OLED), photovoltaic cells using photoelectric effect, touch screens, or the like require a transparent conductive electrode, i.e. a conductive material which transmits light.
A transparent conductive film is one of key materials that are essential for flat panel displays, photovoltaic cells, or the like. The transparent conductive film serves to protect internal electronic devices from external influences, transfer signals and current to electronic devices, and transmit light emitted from the electronic devices to a screen without resistance. The transparent conductive film is required to have superior transmission and electrical conductivity. A material used for such a transparent conductive film must have a low resistivity (10−3 to 10−4 Ωcm) and a high light transmittance in the visible light range. In addition, the characteristics of the material that is used for the transparent conductive film are required to change little due to heat during the fabrication process of the internal electronic devices.
An example of the transparent electrode material that has been most popular to dates is indium tin oxide (ITO: In1-xSnxO3). Although ITO has superior optical properties, it has the following drawbacks: The fabrication price of In, one of its source elements, is very high, and the properties of ITO are significantly changed by heat when it is exposed to plasma.
In contrast, referring to zinc oxide (ZnO) having a band gap of about 3.4 eV, its infrared (IR) and visible light transmittances are very good, and it has superior electrical conductivity and superior endurance to plasma. In addition, ZnO can be grown at a low temperature, and its fabrication price is relatively low. Therefore, ZnO is emerging as a promising material for a transparent electrode of a large display and a functional window.
ZnO can be deposited on a substrate to form a thin film by physical vapor deposition (PVD). When sputtering is selected from among PVD methods, a ZnO-based target is used for a target material. For a precursor for the fabrication of ZnO, a Zn complex to which an organic ligand is bonded is mainly used. Among well-known complexes, Zn(O2CMe)2, Zn4O(O2CNEt2)6 and the like are volatized at a relatively low temperature. However, they cause carbon contamination in the thin film, which is problematic. In addition, while a metal halide compound is widely used as a precursor for the production of ZnO, its low volatility requires a high temperature, which makes processing difficult. In addition, studies on the process of depositing a ZnO-based thin film on a substrate by chemical vapor deposition (CVD) using a source material, such as diethyl zinc (DEZ) or a DEZ octane solution, have also been carried out.
FIG. 1 is a configuration view schematically showing a plasma-enhanced chemical vapor deposition (PECVD) apparatus which deposits a ZnO-based thin film using as a related-art source material of DEZ or dimethyl zinc (DMZ). FIG. 1 illustrates a PECVD apparatus which deposits undoped ZnO and F- and B-doped ZnO. The PECVD apparatus shown in FIG. 1 forms a reaction composition by combining DEZ or DMZ as a fugitive organic metal zinc compound, Ar or He as a carrier gas, CO2 as an oxidizer, and tetraethyl boron (TEB) or nitrogen trifluoride (NF3) as a dopant, and blows the reaction composition into a deposition chamber 1, thereby depositing a ZnO-based thin film on a substrate 5. Among reference numerals which have not been described, 2 indicates an upper electrode, 3 indicates a lower electrode, 4 indicates a hole, 6 indicates an opening, 7 indicates a power source, 8, 9, 10, 11, 12 and 13 indicate lines, 14, 15, 16, 17, 18 and 19 indicate mass flow controllers (MFCs), and 20 indicates a thermostat.
FIG. 2 is a cross-sectional view schematically showing a deposition chamber which deposits a ZnO-based thin film using a related-art source material, i.e. a solution produced by dissolving DEZ into an organic solvent. A solution that was produced by dissolving DEZ into an organic solvent, such as ether, ketone, ester, hydrocarbon or alcohol, is vaporized. The vaporized solution is supplied into a deposition chamber via a duct 24, and at the same time, an oxidizer gas, such as oxygen gas, ozone gas, nitrogen oxide gas or water vapor, is supplied into the deposition chamber via a duct 25. Among reference numerals which have not been described, 21 indicates a substrate, 22 indicates a susceptor, 23 indicates a heater, 26 indicates a rotary shaft, 27 indicates a reactant gas outlet, and 29 indicates a reaction chamber.
However, when DEZ or DMZ is used as in FIG. 1, there are problems in that the vapor pressure is too high, that the danger of ignition is significant owing to high reactivity, and that it is not easy to control the composition of the thin film. In particular, there are disadvantages in that the deposition of the ZnO-based thin film using a precursor, such as DEZ or DMZ, must be carried out under low pressure, and that atmospheric pressure chemical vapor deposition (APCVD) cannot be used. Therefore, as shown in FIG. 2, the method of suppressing the natural volatility and explosiveness and forming a high-purity ZnO thin film by dissolving DEZ or DMZ into an organic solution has also been studied. However, since the precursor and the diluted solvent have different vapor pressures, this method requires chemical deposition to be performed by vaporizing the source material after supplying the source material into a vaporizer, which is problematic. In addition, when the source material is imperfectly vaporized, there is high possibility that impurities may be deposited inside the vaporizer due to imperfect decomposition of the source material, thereby clogging the vaporizer or causing the reproducibility of a thin film to be significantly inferior.
The information disclosed in the Background of the Invention section is provided only for better understanding of the background of the invention, and should not be taken as an acknowledgment or any form of suggestion that this information forms a prior art that would already be known to a person skilled in the art.